It is well known that upon the color development of a silver halide photographic light-sensitive material, after exposure, an oxidized aromatic primary amine developing agent can be reacted with a dye forming coupler to obtain a color image.
It is also known that, for the color development of a silver halide color photographic material, an oxidized aromatic primary amine developing agent can be reacted with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine, and the like, thus forming a color image. In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green and red lights, and yellow, magenta and cyan color image formers, which are respectively the complementary colors of blue, green and red, are employed. For example, a coupler of the acylacetanilide or benzoylmethane type is used for forming a yellow color image; a coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type is generally used for forming a magenta color image; and a coupler of the phenol type, such as a phenol and a naphthol, is generally used for forming a cyan color image.
It is also required in a multilayer color photographic light-sensitive material that each coupler is fixed in a layer separated from each other in order to reduce color mixing and improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method is to introduce a long chain aliphatic group into a coupler molecule in order to prevent diffusion. Couplers according to such a method require a step of addition to an aqueous gelatin solution by solubilizing in alkali, or a step of dispersing in an aqueous gelatin solution by dissolving in an organic solvent having a high boiling point, since the couplers are immiscible with an aqueous gelatin solution. Such color couplers may cause crystal formation in a photographic emulsion. Furthermore, when using an organic solvent having a high boiling point, a large amount of gelatin must be employed since the organic solvent having a high boiling point makes an emulsion layer soft. Consequently, this increases the thickness of the material even though it is desirable to reduce the thickness of the emulsion layer.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler latex obtained by polymerization of a monomeric coupler. An example of a method for adding a polymer coupler in a latex form to a hydrophilic colloid composition is a method in which a latex prepared by an emulsion polymerization method is directly added to a gelatino silver halide emulsion and a method in which an oleophilic polymer coupler obtained by polymerization of a monomeric coupler is dispersed in a latex form in an aqueous gelatin solution. Some examples of the former emulsion polymerization methods include an emulsion polymerization method in an aqueous gelatin phase as described in U.S. Pat. No. 3,370,952 and an emulsion polymerization method in water as described in U.S. Pat. No. 4,080,211. An example of the latter method in which an oleophilic polymer coupler is dispersed in a latex form is described in U.S. Pat. No. 3,451,820.
The addition of cyan polymer couplers in a latex form to a gelatino silver halide emulsion layer is known as described in West German Pat. No. 2,725,591, U.S. Pat. Nos. 3,926,436 and 3,767,412 and Research Disclosure, No. 21728 (1982), in addition to the above-described patents.
The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. First, the strength of the film formed is not deteriorated, because the hydrophobic substance is in a latex form. Second, since the latex can contain coupler monomers in a high concentration, it is easy to incorporate couplers in a high concentration into a photographic emulsion, and the crystallization of couplers in the emulsion layer is eliminated. Third, since the increase of viscosity is small, it is possible to reduce the thickness of the emulsion layer which results in the improvement in sharpness. Fourth, color mixing is prevented, since a polymer coupler is completely immobilized.
However, these polymer coupler latexes have unsolved problems as well as many excellent features such as those described above. In particular, the problem of a cyan polymer coupler latex is color stain which occurs upon irradiation of light to color photographic material containing the cyan polymer coupler latex (hereinafter referred to as light stain).
Since a color photographic material contains many organic compounds which include a coupler as a representative example, these organic compounds are decomposed to form various kinds of colored substances when the color photographic material is irradiated with light. The colored substances are the origin of the light stain, particularly in non-image areas or areas of low optical density.
Many techniques for preventing the occurrence of light stain have been known. For example, a method is known in which a 2-(2'-hydroxyphenyl)benzotriazole compound is incorporated into a photographic silver halide emulsion layer to prevent the occurrence of light stain as described in U.S. Pat. No. 3,253,921.
However, this method is not always sufficient because the effect on preventing light stain decreases somewhat when the 2-(2'-hydroxyphenyl)benzotriazole compound is added in a large amount or the color forming property of the coupler is reduced.